To secure a breakdown voltage of a low breakdown voltage metal-oxide-semiconductor field-effect-transistor (MOSFET) with a field plate structure, it is necessary to deepen a trench and increase a thickness of a field plate insulating film, and it is necessary to increase a volume of the trench. For this reason, a current path of a drift layer is narrowed due to the trench, and movement of carriers is prevented, so that a trade-off occurs in which on-resistance increases. To avoid this problem, it is an important task to reduce the on-resistance of the drift layer by making the trench as narrow as possible. For example, research has been conducted to reduce a width of a source electrode to secure a width of the drift layer.